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Scottdagoalie
Scottdagoalie, Senior Master Tech.
Category: Ford
Satisfied Customers: 1940
Experience:  30 years with Ford dealers
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PO603

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PO603
HiCustomer Thank you for asking your question on JustAnswer. The other Experts and I are working on your answer. By the way, it would help us to know:

-What year is your Ford?
-There are no P0603 codes in the 1996 service manual.

Thank you again for trusting us with your problem. Please reply as soon as possible so that we can finish answering your question.
Customer: replied 7 years ago.
THIS IS A 1996 F250 7.3 POWER STROKE I HAVE THIS CODE AND WILL NOT START. IT WAS GOING DOWN THE ROAD WHEN IT JUST QUITE, IT FIRST HAD A CAM SENSOR CODE SO I REPLACED IT, NO GO, THAT CODE WENT AWAY,THEN THIS CODE POPED UP.

The code P0603 refers to no keep alive power to the PCM.This can be set by a faulty PCM or by power interuption to the PCM.Given that the truck doesn't start,I suggest checking for power to the PCM.

 

AH1 CONTINUOUS DTC P0603 IS SET WHEN THE PCM HAS LOST KAPWR

    Note: This code may have been caused by disconnecting the PCM or the batteries.

  • Possible causes:
    • Battery or PCM has been disconnected.
    • Battery cables loose or poor connection.
    • Battery discharged.
    • Open in KAPWR circuit.
    • Blown fuse.
    • PCM.
  • Check for other codes.
  • Key on, engine off.
  • Clear DTCs.
  • Cycle key off, then on.
  • Perform Retrieve Continuous DTCs.

Was DTC P0603 present?

Yes No
GO to AH2 . Intermittent failure, unable to duplicate. REPAIR other DTCs as necessary. If none, testing is complete. RESTORE vehicle. CLEAR DTCs and RETEST.

AH2 CHECK 5 AMP FUSE (#2 FOR F-SERIES) OR (#27 FOR ECONOLINE)

  • Key off.
  • Measure voltage between KAPWR (MINI Fuse 2 on F-Series) or (MINI Fuse 27 on Econoline) and battery ground.

Is battery voltage present on both sides of the fuse?

Yes No
GO to AH3 . REPAIR short to ground on Circuit 729 (R/W) for F-Series or Circuit 37 (Y) for Econoline. RESTORE vehicle. CLEAR DTCs and RETEST.

AH3 CHECK FOR VOLTAGE TO PCM

  • Key off.
  • Install breakout box, leave PCM disconnected.
  • Measure voltage between PCM Test Pin 55 and ground Pins 25, 51, 76, 77, 91 and 103.

Is B+ present?

Yes No
RESTORE vehicle; CLEAR DTC, RERUN test, If code reappears, REPLACE the PCM. REPAIR open on KAPWR circuit. RESTORE vehicle. CLEAR DTCs and RETEST.

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